rt: introduce routing expression

Introduce rt expression for routing related data with support for nexthop
(i.e. the directly connected IP address that an outgoing packet is sent
to), which can be used either for matching or accounting, eg.

 # nft add rule filter postrouting \
	ip daddr 192.168.1.0/24 rt nexthop != 192.168.0.1 drop

This will drop any traffic to 192.168.1.0/24 that is not routed via
192.168.0.1.

 # nft add rule filter postrouting \
	flow table acct { rt nexthop timeout 600s counter }
 # nft add rule ip6 filter postrouting \
	flow table acct { rt nexthop timeout 600s counter }

These rules count outgoing traffic per nexthop. Note that the timeout
releases an entry if no traffic is seen for this nexthop within 10 minutes.

 # nft add rule inet filter postrouting \
	ether type ip \
	flow table acct { rt nexthop timeout 600s counter }
 # nft add rule inet filter postrouting \
	ether type ip6 \
	flow table acct { rt nexthop timeout 600s counter }

Same as above, but via the inet family, where the ether type must be
specified explicitly.

"rt classid" is also implemented identical to "meta rtclassid", since it
is more logical to have this match in the routing expression going forward.

Signed-off-by: Anders K. Pedersen <akp@cohaesio.com>
Signed-off-by: Pablo Neira Ayuso <pablo@netfilter.org>

7 files changed, 228 insertions, 0 deletions

diff --git a/src/Makefile.am b/src/Makefile.am
index 63bbef2c..9a151bd4 100644
--- a/src/Makefile.am
+++ b/src/Makefile.am
@@ -38,6 +38,7 @@ nft_SOURCES =	main.c				\
 		exthdr.c			\
 		hash.c				\
 		meta.c				\
+		rt.c				\
 		numgen.c			\
 		ct.c				\
 		netlink.c			\
diff --git a/src/evaluate.c b/src/evaluate.c
index 45af3298..ab0dd9ef 100644
--- a/src/evaluate.c
+++ b/src/evaluate.c
@@ -612,6 +612,38 @@ static int expr_evaluate_payload(struct eval_ctx *ctx, struct expr **exprp)
 }
 
 /*
+ * RT expression: validate protocol dependencies.
+ */
+static int expr_evaluate_rt(struct eval_ctx *ctx, struct expr **expr)
+{
+	const struct proto_desc *base;
+	struct expr *rt = *expr;
+
+	rt_expr_update_type(&ctx->pctx, rt);
+
+	base = ctx->pctx.protocol[PROTO_BASE_NETWORK_HDR].desc;
+	switch (rt->rt.key) {
+	case NFT_RT_NEXTHOP4:
+		if (base != &proto_ip)
+			goto err;
+		break;
+	case NFT_RT_NEXTHOP6:
+		if (base != &proto_ip6)
+			goto err;
+		break;
+	default:
+		break;
+	}
+
+	return expr_evaluate_primary(ctx, expr);
+
+err:
+	return expr_error(ctx->msgs, rt,
+			  "ether type ip or ip6 must be specified before "
+			  "routing expression");
+}
+
+/*
  * CT expression: update the protocol dependant types bases on the protocol
  * context.
  */
@@ -1609,6 +1641,8 @@ static int expr_evaluate(struct eval_ctx *ctx, struct expr **expr)
 		return expr_evaluate_primary(ctx, expr);
 	case EXPR_PAYLOAD:
 		return expr_evaluate_payload(ctx, expr);
+	case EXPR_RT:
+		return expr_evaluate_rt(ctx, expr);
 	case EXPR_CT:
 		return expr_evaluate_ct(ctx, expr);
 	case EXPR_PREFIX:
diff --git a/src/netlink_delinearize.c b/src/netlink_delinearize.c
index c3b0b278..dc9cc837 100644
--- a/src/netlink_delinearize.c
+++ b/src/netlink_delinearize.c
@@ -585,6 +585,21 @@ static void netlink_parse_meta(struct netlink_parse_ctx *ctx,
 		netlink_parse_meta_stmt(ctx, loc, nle);
 }
 
+static void netlink_parse_rt(struct netlink_parse_ctx *ctx,
+			     const struct location *loc,
+			     const struct nftnl_expr *nle)
+{
+	enum nft_registers dreg;
+	uint32_t key;
+	struct expr *expr;
+
+	key  = nftnl_expr_get_u32(nle, NFTNL_EXPR_RT_KEY);
+	expr = rt_expr_alloc(loc, key, false);
+
+	dreg = netlink_parse_register(nle, NFTNL_EXPR_RT_DREG);
+	netlink_set_register(ctx, dreg, expr);
+}
+
 static void netlink_parse_numgen(struct netlink_parse_ctx *ctx,
 				 const struct location *loc,
 				 const struct nftnl_expr *nle)
@@ -1086,6 +1101,7 @@ static const struct {
 	{ .name = "payload",	.parse = netlink_parse_payload },
 	{ .name = "exthdr",	.parse = netlink_parse_exthdr },
 	{ .name = "meta",	.parse = netlink_parse_meta },
+	{ .name = "rt",		.parse = netlink_parse_rt },
 	{ .name = "ct",		.parse = netlink_parse_ct },
 	{ .name = "counter",	.parse = netlink_parse_counter },
 	{ .name = "log",	.parse = netlink_parse_log },
@@ -1724,6 +1740,7 @@ static void expr_postprocess(struct rule_pp_ctx *ctx, struct expr **exprp)
 		break;
 	case EXPR_SET_REF:
 	case EXPR_META:
+	case EXPR_RT:
 	case EXPR_VERDICT:
 	case EXPR_NUMGEN:
 		break;
diff --git a/src/netlink_linearize.c b/src/netlink_linearize.c
index b04625f1..a5d4502f 100644
--- a/src/netlink_linearize.c
+++ b/src/netlink_linearize.c
@@ -172,6 +172,18 @@ static void netlink_gen_meta(struct netlink_linearize_ctx *ctx,
 	nftnl_rule_add_expr(ctx->nlr, nle);
 }
 
+static void netlink_gen_rt(struct netlink_linearize_ctx *ctx,
+			     const struct expr *expr,
+			     enum nft_registers dreg)
+{
+	struct nftnl_expr *nle;
+
+	nle = alloc_nft_expr("rt");
+	netlink_put_register(nle, NFTNL_EXPR_RT_DREG, dreg);
+	nftnl_expr_set_u32(nle, NFTNL_EXPR_RT_KEY, expr->rt.key);
+	nftnl_rule_add_expr(ctx->nlr, nle);
+}
+
 static void netlink_gen_numgen(struct netlink_linearize_ctx *ctx,
 			    const struct expr *expr,
 			    enum nft_registers dreg)
@@ -641,6 +653,8 @@ static void netlink_gen_expr(struct netlink_linearize_ctx *ctx,
 		return netlink_gen_exthdr(ctx, expr, dreg);
 	case EXPR_META:
 		return netlink_gen_meta(ctx, expr, dreg);
+	case EXPR_RT:
+		return netlink_gen_rt(ctx, expr, dreg);
 	case EXPR_CT:
 		return netlink_gen_ct(ctx, expr, dreg);
 	case EXPR_SET_ELEM:
diff --git a/src/parser_bison.y b/src/parser_bison.y
index ec9052af..dc02fd23 100644
--- a/src/parser_bison.y
+++ b/src/parser_bison.y
@@ -338,6 +338,9 @@ static void location_update(struct location *loc, struct location *rhs, int n)
 %token OIFGROUP			"oifgroup"
 %token CGROUP			"cgroup"
 
+%token CLASSID			"classid"
+%token NEXTHOP			"nexthop"
+
 %token CT			"ct"
 %token DIRECTION		"direction"
 %token STATE			"state"
@@ -590,6 +593,10 @@ static void location_update(struct location *loc, struct location *rhs, int n)
 %destructor { expr_free($$); }	meta_expr
 %type <val>			meta_key	meta_key_qualified	meta_key_unqualified	numgen_type
 
+%type <expr>			rt_expr
+%destructor { expr_free($$); }	rt_expr
+%type <val>			rt_key
+
 %type <expr>			ct_expr
 %destructor { expr_free($$); }	ct_expr
 %type <val>			ct_key		ct_key_dir	ct_key_counters
@@ -1995,6 +2002,7 @@ primary_expr		:	symbol_expr			{ $$ = $1; }
 			|	payload_expr			{ $$ = $1; }
 			|	exthdr_expr			{ $$ = $1; }
 			|	meta_expr			{ $$ = $1; }
+			|	rt_expr				{ $$ = $1; }
 			|	ct_expr				{ $$ = $1; }
 			|	numgen_expr			{ $$ = $1; }
 			|	hash_expr			{ $$ = $1; }
@@ -2529,6 +2537,16 @@ hash_expr		:	JHASH	expr	MOD	NUM	SEED	NUM
 			}
 			;
 
+rt_expr			:	RT	rt_key
+			{
+				$$ = rt_expr_alloc(&@$, $2, true);
+			}
+			;
+
+rt_key			:	CLASSID		{ $$ = NFT_RT_CLASSID; }
+			|	NEXTHOP		{ $$ = NFT_RT_NEXTHOP4; }
+			;
+
 ct_expr			: 	CT	ct_key
 			{
 				$$ = ct_expr_alloc(&@$, $2, -1);
diff --git a/src/rt.c b/src/rt.c
new file mode 100644
index 00000000..232c1dcb
--- /dev/null
+++ b/src/rt.c
@@ -0,0 +1,141 @@
+/*
+ * Routing expression related definition and types.
+ *
+ * Copyright (c) 2016 Anders K. Pedersen <akp@cohaesio.com>
+ *
+ * This program is free software; you can redistribute it and/or modify
+ * it under the terms of the GNU General Public License version 2 as
+ * published by the Free Software Foundation.
+ */
+
+#include <errno.h>
+#include <stddef.h>
+#include <stdlib.h>
+#include <stdio.h>
+#include <stdint.h>
+#include <string.h>
+#include <arpa/inet.h>
+#include <linux/netfilter.h>
+
+#include <nftables.h>
+#include <expression.h>
+#include <datatype.h>
+#include <rt.h>
+#include <rule.h>
+
+static struct symbol_table *realm_tbl;
+static void __init realm_table_init(void)
+{
+	realm_tbl = rt_symbol_table_init("/etc/iproute2/rt_realms");
+}
+
+static void __exit realm_table_exit(void)
+{
+	rt_symbol_table_free(realm_tbl);
+}
+
+static void realm_type_print(const struct expr *expr)
+{
+	return symbolic_constant_print(realm_tbl, expr, true);
+}
+
+static struct error_record *realm_type_parse(const struct expr *sym,
+					     struct expr **res)
+{
+	return symbolic_constant_parse(sym, realm_tbl, res);
+}
+
+static const struct datatype realm_type = {
+	.type		= TYPE_REALM,
+	.name		= "realm",
+	.desc		= "routing realm",
+	.byteorder	= BYTEORDER_HOST_ENDIAN,
+	.size		= 4 * BITS_PER_BYTE,
+	.basetype	= &integer_type,
+	.print		= realm_type_print,
+	.parse		= realm_type_parse,
+	.flags		= DTYPE_F_PREFIX,
+};
+
+static const struct rt_template rt_templates[] = {
+	[NFT_RT_CLASSID]	= RT_TEMPLATE("classid",
+					      &realm_type,
+					      4 * BITS_PER_BYTE,
+					      BYTEORDER_HOST_ENDIAN,
+					      false),
+	[NFT_RT_NEXTHOP4]	= RT_TEMPLATE("nexthop",
+					      &ipaddr_type,
+					      4 * BITS_PER_BYTE,
+					      BYTEORDER_BIG_ENDIAN,
+					      true),
+	[NFT_RT_NEXTHOP6]	= RT_TEMPLATE("nexthop",
+					      &ip6addr_type,
+					      16 * BITS_PER_BYTE,
+					      BYTEORDER_BIG_ENDIAN,
+					      true),
+};
+
+static void rt_expr_print(const struct expr *expr)
+{
+	printf("rt %s", rt_templates[expr->rt.key].token);
+}
+
+static bool rt_expr_cmp(const struct expr *e1, const struct expr *e2)
+{
+	return e1->rt.key == e2->rt.key;
+}
+
+static void rt_expr_clone(struct expr *new, const struct expr *expr)
+{
+	new->rt.key = expr->rt.key;
+}
+
+static const struct expr_ops rt_expr_ops = {
+	.type		= EXPR_RT,
+	.name		= "rt",
+	.print		= rt_expr_print,
+	.cmp		= rt_expr_cmp,
+	.clone		= rt_expr_clone,
+};
+
+struct expr *rt_expr_alloc(const struct location *loc, enum nft_rt_keys key,
+			   bool invalid)
+{
+	const struct rt_template *tmpl = &rt_templates[key];
+	struct expr *expr;
+
+	if (invalid && tmpl->invalid)
+		expr = expr_alloc(loc, &rt_expr_ops, &invalid_type,
+				  tmpl->byteorder, 0);
+	else
+		expr = expr_alloc(loc, &rt_expr_ops, tmpl->dtype,
+				  tmpl->byteorder, tmpl->len);
+	expr->rt.key = key;
+
+	return expr;
+}
+
+void rt_expr_update_type(struct proto_ctx *ctx, struct expr *expr)
+{
+	const struct proto_desc *desc;
+
+	switch (expr->rt.key) {
+	case NFT_RT_NEXTHOP4:
+		desc = ctx->protocol[PROTO_BASE_NETWORK_HDR].desc;
+		if (desc == &proto_ip)
+			expr->dtype = &ipaddr_type;
+		else if (desc == &proto_ip6) {
+			expr->rt.key++;
+			expr->dtype = &ip6addr_type;
+		}
+		expr->len = expr->dtype->size;
+		break;
+	default:
+		break;
+	}
+}
+
+static void __init rt_init(void)
+{
+	datatype_register(&realm_type);
+}
diff --git a/src/scanner.l b/src/scanner.l
index 8afddf15..c8352014 100644
--- a/src/scanner.l
+++ b/src/scanner.l
@@ -446,6 +446,9 @@ addrstring	({macaddr}|{ip4addr}|{ip6addr})
 "oifgroup"		{ return OIFGROUP; }
 "cgroup"		{ return CGROUP; }
 
+"classid"		{ return CLASSID; }
+"nexthop"		{ return NEXTHOP; }
+
 "ct"			{ return CT; }
 "l3proto"		{ return L3PROTOCOL; }
 "proto-src"		{ return PROTO_SRC; }